Digital cameras and mobile phones that include solid-state imaging elements and thus have an imaging function have high added value. The reduction in size and power consumption as well as the increase in definition has been required for solid-state imaging elements in recent years. Photosensors are used as solid-state imaging elements.
A photosensor using an amplification function of a MOS transistor, called a complementary metal oxide semiconductor (CMOS) sensor, can be fabricated through a general CMOS process. Thus, fabrication costs of a solid-state imaging device including a CMOS sensor in each pixel can be low, and a semiconductor display device including a CMOS sensor and a display element formed over one substrate can be provided. Further, the drive voltage of a CMOS sensor is lower than that of a charge coupled device (CCD) sensor, so that power consumption of the solid-state imaging device can be kept low.
Patent Document 1 discloses an imaging device including a CMOS sensor.